The invention relates to a method for producing a composite body having a self-supporting surface.
It is known how to produce self-supporting surfaces by means of coating methods. For example, a method is known from DE 33 15 407 A1 where for heat exchangers for example, cavities or closed ducts are sealed from the outside using cover layers produced by electroplating. Elongated fillers are inserted into the cavities or ducts to be coated and are later removed, and at one end project from the cavity or the duct, wherein the remaining space inside the cavity or duct around each filler is filled with wax. After removal of the filler, the opening in the wax resulting from its removal is sealed with a wax plug and the covering layer is applied by galvanization.
U.S. Pat. No. 3,364,548 discloses a method for producing a heat exchanger by electroforming. A negative mold is provided by stacking thin copper sheets and thick aluminum sheets one on top of the other. The stack has a rectangular cross-section. The top and the bottom of the stack are of copper sheet. The copper sheets project beyond the aluminum sheets, wherein the thickness of the aluminum sheets corresponds to the later required duct cross-sections. The unevennesses of the side walls of the stack are removed by spraying a thick layer of a soft aluminum alloy onto the side walls of the stack. The sprayed-on aluminum layer not only fills in the unevennesses on the side walls, but holds the stack together axially.
The coated side walls are smoothed such that the edges of the copper sheets become visible on the surface of the side walls. This is then followed by selective pickling of the sprayed-on aluminum layer by about 250 μm to about 750 μm. A copper layer of about 750 μm to 1000 μm thickness is then applied to the side walls, wherein the previously exposed edges of the copper sheet are buried in the copper layer. The thickness of the copper layer is selected to match the required robustness and compressive strength of the heat exchanger.
The stack is beveled at its narrow sides such that the aluminum sheets in the interior of the stack are likewise beveled and their beveled edges are exposed, wherein a copper web remains in the center of the narrow side. The beveled surfaces are masked such that masked surfaces and exposed aluminum surfaces are obtained. The adjacently positioned beveled narrow sides are masked in a height-offset manner, such that the exposed edges of the aluminum sheets predetermine height-offset ducts of the heat exchanger. The stack is in turn coated with copper and the exposed aluminum sheets are dissolved out, such that a copper framework inside a copper envelope remains to form the heat exchanger.
It is desirable to provide a method for producing a composite body made of at least one self-supporting surface and at least one element connected to the surface in a coating process, wherein a stable connection can be created between the self-supporting surface and the element.
A method is proposed for producing a composite body comprising at least one self-supporting surface and at least one element connected to the surface in a coating process, wherein a negative mold is provided which has the at least one element of the composite body and wherein the following steps are performed:
(a) smoothing the negative mold (10) on a surface (18) to be coated as a whole prior to a selective ablation in order to set the at least one element in the negative mold (10) to a required dimension;
(b) selectively ablating the surface of the negative mold to be coated with the at least one self-supporting surface by a defined first thickness such that the at least one element stands out from the surface as a projection at least in some areas, wherein the first thickness (d14) is between 5 μm and 25 μm;
(c) depositing one or more layers for forming the at least one self-supporting surface having a defined second thickness, wherein an elevation forms in the area of the projection of the at least one element and the projection (22) of the at least one element (20, 20a, 20b, 20c) is embedded in the surface (30), wherein the surface (30) has a thickness of a few tens of μm;
(d) leveling the coated surface, wherein the elevation is removed and a surface (40) of homogeneous appearance is formed; and
(e) selectively removing at least parts of the negative mold.
Advantageously, a firm connection of the at least one element to the surface can be produced. The surface can have a thickness of only a few tens of micrometers. By specifying an appropriate oversize, a high dimensional accuracy of the negative mold and the surface can be achieved. The top of the surface can be treated without influencing the adhesion between the at least one element and the surface. In particular, finish-turning of the negative mold as a whole is possible, such that the at least one element in the negative mold can be brought to a required dimension. The method in accordance with the invention is particularly suitable for connecting one or more thin-walled elements to a foil of comparable wall thickness, e.g. for connection of one or more elements each having a thickness of a few 10 μm to a foil of comparable thickness.
A selective ablation prior to coating can be advantageously performed using wet chemicals, for example by chemical pickling, by electrolytic pickling, by an electrolytic polishing bath and the like, however other methods are also conceivable, for example with vacuum methods, in particular when only low thicknesses have to be ablated, for example by means of cathode sputtering or plasma-assisted etching, or for greater thicknesses for example by sandblasting, glass blasting and the like. An ablation of 5-25 μm, preferably between about 10 and 20 μm is favorable.
The deposition of the at least one layer can be performed with various methods. For example the coating can be performed using PVD methods such as cathode sputtering, vapor deposition and/or CVD methods such as reactive plasma-assisted vacuum coating methods, or also with current-free or electrochemical galvanic processes. One or more layers embed the at least one element inside the deposited layers at its projecting end. A stable connection is produced between the at least one element and the surface. The one or more layers can be insulating, semi-conducting and/or metallic. The person skilled in the art will select a suitable method or a suitable combination of various methods for the respectively required embodiment of the composite body as regards layer thickness and material.
In accordance with an advantageous method step, the deposition of the one or more layers onto the negative mold can be achieved by electroforming. Electroforming permits a readily controllable and reproducible deposition of layers having thicknesses in the range of several tells of micrometers.
In accordance with an advantageous method step, the negative mold can be smoothed before the selective ablation on the surface to be coated as a whole, e.g. finish-turned and/or ground. A simple handling of the negative mold composed of several parts is enabled. In particular, the elements can, during assembly with the parts of the negative mold, have a greater diameter and do not need to be adapted right from the start to the dimension of the negative mold. The parts can be considerably thicker than the element(s) and thus ensure stability of the negative mold, which therefore can also be readily machined. The adaptation to a common dimension of element(s) and parts is achieved by smoothing of the surface, wherein protruding areas are ablated. This permits a high dimensional accuracy of the negative mold. It is however also conceivable, alternatively or additionally, to roughen the surface after finish-turning of the negative mold, depending on the required inner surface of the subsequently self-supporting surface.
In accordance with an advantageous method step, the selective ablation of the negative mold can be performed by a wet-chemical treatment, for example with an alkaline pickle. A defined chemical ablation of the ablatable areas of the negative mold can thus be performed under defined conditions, wherein the at least one element remains unaffected or at least has only a considerably lower etching rate than the ablatable areas of the negative mold.
In accordance with an advantageous method step, the negative mold can be produced with an oversize relative to a final dimension of the negative mold. This allows the surface to be ablated by selective ablation to the required final dimension of the negative mold. The oversize can be adjusted to match an ablation rate during the selective ablation, such that the method can be adapted to different materials and pickles in a simple manner.
In accordance with an advantageous method step, the surface can have a greater thickness than the projection of the at least one element. In this case, the projection of the at least one element can be eliminated.
In accordance with an advantageous method step, the surface can have a thickness greater by a factor of 5 than the projection of the at least one element. It is clear that the projection is already less pronounced due to the high layer thickness and somewhat leveled.
In accordance with an advantageous method step, the surface can be formed from a first and a second layer, wherein the first layer has a lower thickness than the second. The first layer can be advantageously at most half as thick as the second one. The first layer can produce an advantageous adhesion to the at least one element. The first layer can therefore be formed from the same material as the at least one element. The second layer can then be selected to have particularly favorable properties for the surface treatment of the later self-supporting surface, for example to act as a functional layer or the like.
In accordance with an advantageous method step, the elevation can be ablated in that the coated negative mold is overall finish-turned and/or ground. Thanks to the fact that the layer sequence deposited on the negative mold is thicker than the projection, the elevation can be removed without impairing the embedding of the at least one element into the coating. It is even possible to achieve a reflecting surface. Machining of the surface is advantageously made easier, since the coating is permanently connected by the element embedded in some areas with the negative mold.
In accordance with an advantageous method step, a surface treatment can precede the galvanic deposition to increase the adhesive strength between the at least one element and the surface. For example, the surface can be roughened or an adhesion promoting layer applied to it.
In accordance with an advantageous method step, the surface can be polished before removal of the negative mold. The surface is stabilized by the negative mold as it is permanently connected to the negative mold.
In accordance with an advantageous method step, the negative mold can be removed by selective chemical etching. The negative mold can therefore also be removed through complex structures of the at least one element that are not accessible to machining. The negative mold can be removed without the at least one element being removed. Optionally, a coloring step can follow in which the at least one element is colored, for example to obtain an increased absorption or achieve a required color impression.
In accordance with an advantageous method step, the surface can be produced from a layer of copper or a copper-containing component and from a layer of nickel or a nickel-containing component deposited thereon. Nickel has the advantageous property of leveling uneven areas with a high layer thickness and of forming a glossy surface.
In a favorable case, the at least one element can be produced from copper or a copper-containing component. Copper is for example relatively inexpensive, has a high thermal conductivity and can be easily treated, e.g. colored, to create optical effects, such as increased absorption, a color impression and the like.
In a favorable case, the negative mold can be produced at least in some areas from aluminum. For example, the negative mold can be produced in that an aluminum part and an element to be connected to the self-supporting surface are joined together alternatingly in a stacking direction to form a stack and that the stack is subjected to a compressive stress in the stacking direction. The stack forms a stable and easy to handle multi-part negative mold that can be excellently machined.
It is particularly advantageous that the invention can be used for producing a composite body from at least one self-supporting surface and at least one element connected to the surface in a coating process, the body being produced by the following steps:
(a) providing a negative mold comprising the at least one element of the composite body,
(b) selectively ablating a surface of the negative mold to be coated with the at least one self-supporting surface by a defined first thickness such that the at least one element stands out from the surface as a projection at least in some areas,
(c) depositing one or more layers for forming the at least one self-supporting surface having a defined second thickness, wherein an elevation forms in the area of the projection of the at least one element,
(d) leveling the coated surface, wherein the elevation is removed, selectively removing at least parts of the negative mold.
Advantageously, composite bodies for a wide range of applications can be provided, for example for optical components, for decorative applications and the like.
Elements which are identical or have identical effects are provided in the drawings with the same reference numbers.